<template>
    <div class="scroll-container" ref="scrollContainer" @wheel.prevent="handleScroll">
        <div class="scroll-wrapper" ref="scrollWrapper" :style="{top: top+'px'}">
            <slot></slot>
        </div>
    </div>
</template>

<script>
const delta = 15
export default {
    name: 'scrollBar',
    data() {
        return {
            top: 0
        }
    },
    methods: {
        handleScroll(e) {
            const eventDelta = e.wheelDelta || -e.deltaY * 3
            const $container = this.$refs.scrollContainer
            const $containerHeight = $container.offsetHeight
            const $wrapper = this.$refs.scrollWrapper
            const $wrapperHeight = $wrapper.offsetHeight
            if (eventDelta > 0) {
                this.top = Math.min(0, this.top + eventDelta)
            } else {
                if ($containerHeight - delta < $wrapperHeight) {
                    if (this.top < -($wrapperHeight - $containerHeight + delta)) {
                        this.top = this.top
                    } else {
                        this.top = Math.max(this.top + eventDelta, $containerHeight - $wrapperHeight - delta)
                    }
                } else {
                    this.top = 0
                }
            }
        }
    }
}
</script>

<style rel = "stylesheet/scss" lang="scss" scoped> 
@import '../../styles/variables.scss';
.scroll-container {
    position: relative;
    width: 100%;
    height: 100%;
    background-color: $menuBg;
    .scroll-wrapper {
        position: absolute;
        width: 100%!important;
    }
}
</style>

